This disclosure relates to balancing of turbomachine rotors by the addition of weights, and more particularly to weights' attachment features.
The dynamic balancing of turbine rotors is a well-developed art. Each rotor may have, at one or more longitudinal locations, a circumferential array of mounting features permitting the installation of one or more balance weights.
It is known, for example, to balance a rotor by using a computer controlled apparatus to spin the rotor about its rotational axis and measure the parameters of rotational displacements (vibrations) associated with imbalance. Based upon these measurements, the computer outputs an identification of a particular combination of balance weights to balance the rotor. Specifically, the computer may identify particular weight masses to be installed at one to all of the individual mounting locations defined by the mounting features.
A number of different mounting feature constructions are known. An axially protruding flange is shown in U.S. Pat. No. 6,893,222 of Allam (the '222 patent). A radially inwardly projecting flange is shown in U.S. Pat. No. 8,888,458 of Billings et al. (the '458 patent). The '222 patent and the '458 patent illustrate fastening rivets.
US Patent Publication 2005/0265846A1 of Przytulski et al. (the '846 publication) discloses weights accommodated in a radially outwardly open channel. Each weight assembly comprises a weight having a generally radially oriented internally threaded passageway accommodating the threaded shank of a fastener. An inner diameter (ID) end of the fastener engages a base of the channel. The channel has a relatively broad base and narrow outer diameter (OD) opening or neck so that OD shoulders of the weight are biased into contact with the channel wall along the neck to hold the weight in place. The OD end of the fastener has a feature for engaging a tool to tighten the weight in place. The exemplary weight is installed without the fastener, allowing the weight to be inserted at an angle through the slot opening and then righted. Thereafter, the fastener may be inserted radially. In further variations on this system, the slot has an alternating series of broad and narrow portions. The broad portions allow the weight to be inserted with the fastener (so that the fastener axis is essentially radial). The weight may then be shifted circumferentially to one of the narrow portions of the opening and then actuated to drive the weight radially outward and into engagement with the neck.